Magnetic resonance imaging (MRI) is a technology in which magnetic resonance is utilized for the purpose of imaging. Where an atomic nucleus contains a single proton, as is the case, for example, with the nuclei of the hydrogen atoms that are present throughout the human body, this proton exhibits spin motion and resembles a small magnet. The spin axes of these small magnets lack a definite pattern, and if an external magnetic field is applied, the small magnets will be rearranged according to the magnetic force lines of the external field (e.g., will line up in two directions, either parallel or anti-parallel to the magnetic force lines of the external magnetic field). The direction parallel to the magnetic force lines of the external magnetic field is called the positive longitudinal axis, while the direction anti-parallel to the magnetic force lines of the external magnetic field is called the negative longitudinal axis. The atomic nuclei only have a longitudinal magnetization component, which has both a direction and a magnitude. A radio frequency (RF) pulse of a specific frequency is used to excite the atomic nuclei in the external magnetic field such that spin axes deviate from the positive longitudinal axis or negative longitudinal axis, giving rise to resonance (e.g., the phenomenon of magnetic resonance). Once the spin axes of the excited atomic nuclei have deviated from the positive or negative longitudinal axis, the atomic nuclei have a transverse magnetization component. Once emission of the RF pulse has ended, the excited atomic nucleus emits an echo signal, gradually releasing the absorbed energy in the form of electromagnetic waves, such that a phase and energy level both return to the pre-excitation state. An image may be reconstructed by subjecting the echo signal emitted by atomic nuclei to further processing, such as spatial encoding.
A magnetic resonance imaging (MRI) system includes more than one type of coil, such as a body coil that covers the entire body and a local coil that only covers a certain part of the body. Of these, the body coil is used to generate the RF field B1, and may be excited by a pair of input ports of an excitation source that are orthogonal with respect to the system frequency and have the same amplitude. One of the principal aims of body coil debugging is to eliminate coupling between the two ports in this port pair.
To achieve ideal targets, currently used debugging methods are tedious and difficult, and include adjusting the capacitance on the end ring of the body coil, adjusting the mechanical position of the body coil, and a combination of these two methods. Three adjustable capacitors are introduced at three positions on the end ring where the decoupling effect is influenced significantly. The adjustable capacitors may be finely adjusted by having an adjustment rod protrude through the gap between the body coil and the shielding layer. Since the adjustment range of the adjustable capacitors is limited under harsh target requirements such as high voltage, while the distance between the body coil and the shielding layer is very small, the body coil is to be withdrawn and replaced inside the shielding layer repeatedly, and the mechanical position is to be adjusted. This debugging process not only takes time but also increases the likelihood of mechanical wear.